Sedimentological, geomorphological and geochemical evidence of the last marine ingression in central Magellan Straits-southernmost Chile

Research along the coastal belt of the Magellan Straits was carried out in detail with mapping of morphological units. Attention was given to the study of palaeo-shorelines and different terrace orders of presumed marine and transitional origin (BRAMBATI & DE MURO, 2004; BRAMBATI et alii, 2004a; DE MURO et alii, 2000). On the basis of sedimentological, geological and geomorphological results obtained, we made a zoning of the coastal belts along the Atlantic opening of the Straits which enabled us to print three sheets on a scale of 1:200,000 (BRAMBATI et alii, 2004b; DE MURO et alii, 2004a; DI GRANDE et alii, 2004a). Detailed studies and mapping (scale 1:50,000) of the terraced sequences linked to Holo-Pleistocene glacio-eustatic variations are in course. An atlas of 12 maps topographically based on 28 sections of 1:50,000 scale maps (sheets 35, 50, 53, 67, 68, 69, 70, 84, 86, 101, 103 of the Chilean IGM), was made also using the preliminary cartography by Empresa Nacional de Petroleo (ENAP) and the Chilean IGM, aerial photos by Servicio Aerofotogrammetrico Fuerza Aerea de Chile (SAF) and TM and MSS Landsat satellite images (DE MURO et alii, 2004b, c, d, e; DE MURO & DI GRANDE, 2004b; DI GRANDE et alii, 2004b). The Atlas provides a zoning of the area distribution of the most significant deposits processes and forms relating to the coastal belt between Punta Dungeness and Cabo Froward. Morphogenesis of the area was strictly controlled by the processes associated with the advance and retreat of the Magellano Glacier (CLAPPERTON, 1992) and, subordinately, by the main morphodynamic event represented by post deglaciation marine ingression. The Holocene paleogeographic evolutionary picture of the Patagonia-Tierra del Fuego area is mainly controlled by the imposing phenomenon of glacio-isostasy, though it cannot beruled out that the morphogenesis subsequenct to deglaciation may have been affected by mild neo-tectonic movements. As previously observed, relative marine ingressions that produced terracing of the coasts and backland presumably depend on prevalently positive movements of the whole coastal system, related to the final deglaciation of the region. It is deduced that following deglaciation, a strong parallel uplift of the mean sea level was produced with initally transgressive stratigraphic effects. Isostatic rebound, that probably occurred rather late compared to post-glacial transgression, is superimposed with very complex and articulate phenomena, that are under study at present and will be the subject of future works.